Alberta and Saskatchewan, along with other areas of the world, have large bitumen reserves, which are exploited to produce heavy hydrocarbon feedstocks. These feedstocks are characterized by high concentrations (from 35%-55% by volume) of asphaltene rich residues, and typically have API gravities of below 20°, which makes them too dense and viscous for transport in existing pipelines.
One possible approach in producing a pipelineable product is to perform a full upgrading of the feedstock to a light, sweet synthetic crude. The synthetic crude typically resembles light, sweet conventional crude oils, and is a pipelineable product that is generally accepted by conventional refineries for further processing. However, full upgrading facilities are costly to set up and operate and in general only operations producing more than 100,000 barrels of feedstock per day will be able to take advantage of economies of scale in practicing full upgrading to a pipelineable synthetic crude.
Another approach is to perform a partial upgrading of the feedstock to reduce the density and/or viscosity to an extent that will permit pipeline transport of the partially upgraded product. One problem associated with partial upgrading is that the bitumen may undergo changes in quality that render them less valuable to a downstream upgrader. The downstream upgrader may also incur increased hydrogen consumption due to the need to add hydrogen when upgrading the partially upgraded feedstock. Furthermore, partial upgrading may produce a product that has a high olefinic content. Olefins are unstable hydrocarbons that are potentially unsuitable for pipeline transport.
Operations producing less than 30,000 barrels of feedstock per day will generally find that full upgrading is not economically viable. These operators may opt to dilute their feedstock with a light condensate, separately produced in gas plant operations. The light condensate, sometimes referred to as “diluent”, reduces the viscosity and increases the API gravity of the feedstock to produce a pipelineable product. However, as the volume of heavy hydrocarbon feedstock production has increased, the limited supply of diluent has resulted in increased cost of the diluent, in many cases causing the cost of the pipelined product to exceed the value of the feedstock to downstream upgraders and/or refineries.
Another drawback of using diluents to produce a pipelineable product is that new gasoline specifications limit the value of the diluent to the refinery. The diluent, which may be a very light condensate, may also overload processes used to convert the diluent into gasoline. A more recent trend has been to dilute the feedstock with a similar volume of synthetic crude, which is acceptable for refineries that can handle the special characteristics of the synthetic crude portion. While not currently practiced, a similar impact could be achieved by blending a feedstock with a conventional light crude.
In order to mitigate some of the difficulties associated with using a diluent, the downstream upgrader may recover at least a portion of the diluent that is added by the originating producer and transport the recovered diluent by pipeline, back to the originating producer for reuse. For example, the Corridor Pipeline system in Alberta, Canada transports diluted bitumen from the Muskeg River Mine to the Scotford upgrader over a distance of approximately 450 km using a 24 inch pipeline, which transports 215,000 barrels per day of diluted bitumen. A parallel 12 inch return line is used to transport 65,000 barrels per day of diluent from Scotford back to the Muskeg River Mine for reuse. Clearly, such a return line is costly to set up and operate and may not be economically viable for smaller producers.
There remains a need for processes for treating heavy hydrocarbon feedstocks to produce a product which meets applicable criteria for pipeline transport.